Changes In Vibrational Frequencies Research Articles

Leak Detection in Plastic Water Supply Pipes with a High Signal-to-Noise Ratio Accelerometer

A method for detecting leaks in plastic water supply pipes through analysis of the pipe’s surface vibration using a high signal-to-noise ratio accelerometer is proposed and examined. The method involves identification of the changes in vibration frequencies caused on the pipe by the leak and is developed from and examined with respect to detailed experiments. The results are promising, showing that leak detection in plastic pipes is possible provided that the sensor is placed at a small distance from the leak, since wave attenuation in plastic is strong. The results indicate that the methodology has the potential to be a new and competitive type of mobile leak detection system.

Vibration of carbon nanotubes with defects: order reduction methods.

Order reduction methods are widely used to reduce computational effort when calculating the impact of defects on the vibrational properties of nearly periodic structures in engineering applications, such as a gas-turbine bladed disc. However, despite obvious similarities these techniques have not yet been adapted for use in analysing atomic structures with inevitable defects. Two order reduction techniques, modal domain analysis and modified modal domain analysis, are successfully used in this paper to examine the changes in vibrational frequencies, mode shapes and mode localization caused by defects in carbon nanotubes. The defects considered are isotope defects and Stone-Wales defects, though the methods described can be extended to other defects.

DFT study of structures and hydrogen bonds of imidazolium based halogen-free boron containing dicationic ionic liquids

Halogen containing IL based lubricants are sensitive to the moistures and produce acidic corrosive products. So, there is a growing need towards the development and study of the halogen-free boron based ILs (hf-BILs).In this research, we used the Density Functional Theory (DFT) at the M06-2X/6-31G(d,p)level to study the interactions between 1,3-bis[3-methylimidazolium-yl] pentane dication ([C5(mim)2]2+) and bis(oxalato) borate [BOB]− and bis(malonato) borate [BMLB]− anions (halogen-free Boron based anions). The structures changes in the ion complexes have discussed. The interactions of a dication and anions in the ion pairs (IPs) and ion triplets (ITs) have characterized in terms of changes of vibrational frequencies, NBO charge distribution, reduced density gradient (RDG) analysis, and the stabilization energy E(2) values. The interaction energies, thermodynamic parameters and electronic properties of the isolated ions and their complexes were calculated. Electrostatic potential surface (ESP) studies have also been employed to understand the active sites of isolated ions, IPs and ITs. The results demonstrated that intermolecular hydrogen bonding and electrostatic interactions have a significant role in the stabilizing of the ion pairs and dicationic ionic liquids (DILs). The favorable sites for the cation–anion systems have been determined. The results of this research can shed light on the nature of bonding and interactions between ions to help the design of the new task-specific DILs with a lower impact on the environment.

Role of Synthesis Method on Luminescence Properties of Europium(II, III) Ions in β-Ca2SiO4: Probing Local Site and Structure.

The europium ion probes the symmetry disorder in the crystal structure, although the distortion due to charge compensation in the case of aliovalent dopant remains interesting, especially preparation involves low and high temperatures. This work studies the preparation of the β-Ca2SiO4 (from here on C2S) particle from Pechini (C2SP) and hydrothermal (C2SH) methods, and its luminescence variance upon doping with Eu2+ and Eu3+ ions. The blue shift of the charge-transfer band (CTB) in the excitation spectra indicates a larger Eu3+-O2- distance in Eu3+ doped C2SH. The changes in vibrational frequencies due to stretching and bending vibrations in the FTIR and the Raman spectra and binding energy shift in the XPS analysis confirmed the distorted SiO44- tetrahedra in C2SH. The high hydrothermal temperature and pressure produce distortion, which leads to symmetry lowering although doping of aliovalent ion may slightly change the position of the Ca atoms. The increasing asymmetry ratio value from C2SP to C2SH clearly indicates that the europium ion stabilized in a more distorted geometry. It is also supported by Judd-Ofelt analysis. The concentration quenching and site-occupancy of Eu3+ ions in two nonequivalent sites of C2S were discussed. The charge state and concentration of europium ions in C2SP and C2SH were determined using X-ray photoelectron spectroscopy measurements. The C2S particles were studied by X-ray powder diffraction, FTIR, Raman, BET surface area, TGA/DTA, electron microscopy, XPS, and luminescence spectroscopy. The impact of citrate ion on the morphology and particle size of C2SH has been hypothesized on the basis of the microscopy images. This study provides insights that are needed for further understanding the structure of C2S and thereby improves the applications in optical and biomedical areas and cement hydration.

Changes of Normal Coordinates and Geometrical Parameters of a Molecule in a Laser Field

General formulas are derived that describe the changes in equilibrium distances, valence angles, and vibrational frequencies of a polyatomic molecule in a strong laser field. It is shown that the coordinates of normal vibrations do not change in the second order in the field strength. For a nonlinear triatomic molecule of the type of A2B, the changes of geometrical characteristics and vibrational frequencies are obtained in an explicit form.

Structural and energetic quantum chemical investigations into how the bioactive thiazolidinedione and rhodanine scaffolds interact with cytosine to form part of DNA

The interaction within biologically active complex configurations composed of thiazolidinedione-cytosine (TC) and rhodanine-cytosine (RC) have been fully investigated using B3LYP and M062X methods in conjunction with various basis sets, including 6-311++G(d,p), 6-311++G(2d,2p), 6-311++G(df,pd) and AUG-cc-pVDZ. Dispersion corrections to interaction energies using M06-2X-GD3 and double hybrid density functionals (B2PLYP-GD2, B2PLYP-GD3 and mPW2PLYP-GD2) have also been taken into account. The results showed that the interaction energies, including long range dispersion corrections obtained using double hybrid density functionals, are about 1–2.5 kcal/mol higher than uncorrected ones. Various combinations of all possible sites around the monomers which could lead to formation of stable complex configurations were considered, and then six double hydrogen bonded interactions which are formed in a cyclic pattern were further investigated for both complex configurations between cytosine-thiazolidinedione and cytosine-rhodanine. The intermolecular hydrogen bonds which are involved in forming of cyclic interaction patterns are of NH⋯O(N) and CH⋯O(N) types.The TCS′2S1 and RCS′2S1 complex configurations were found to have the largest interaction energies within all the complex configurations studied for cytosine-thiazolidinedione and cytosine-rhodanine respectively at all computational levels used for the calculation of interaction energies. These two most stable complex configurations formed between the S1 site of the cytosine monomer and the S′2 site of the thiazolidinedione or rhodanine.The BSSE-corrected interaction energy for six cyclic double hydrogen bonded complex configurations, calculated at M062X/6-311++G(df,pd) level range from −11.26 to −16.22 kcal/mol for TC complexes and −11.04 to −15.59 kcal/mol for RC complexes.The stability order within thiazolidinedione-cytosine (TC) complexes is TCS′2S1 > TCS′1S1 > TCS′2S2 > TCS′1S2 > TCS′3S2 > TCS′3S1 in all levels studied. The same trend was observed for the stability order of rhodanine-cytosine (RC) complexes.The NBO results reveal that the charge transfer occurred from cytosine to thiazolidinedione or rhodanine within complex configurations which are formed at S′1S1, S′1S2, S′2S1 and S′2S2 sites, whereas in the case of complex configurations of cytosine with thiazolidinedione or rhodanine at S′3S1 and S′3S2 sites this order was reversed.The atom in molecule theory (AIM) and natural bond orbital analysis (NBO) were used to understand the nature of the interactions within the complex configurations studied. This showed good consistency with the interaction energies. In addition, good correlations between geometrical parameters, interaction energies, topological AIM data and NBO results were obtained. Based on AIM and NBO results, it is concluded that the H-bond interactions are electrostatic and partially covalent. Finally, the relationship between interaction energies and vibrational frequency changes at involved H-bonds was analyzed.

A quantum chemical study of the interactions of uracil as a constituent of ribonucleic acid (RNA) with thiazolidinedione and rhodanine bioactive molecules: an insight into energetic and structural features

In this study, the biologically active configurations composed of Thiazolidinedione–Uracil (TU) and Rhodanine–Uracil (RU) have been fully investigated from the energetic and structural points of view, employing B3LYP and M062X functionals in combination with the different basis sets. Dispersion corrections to the interaction energy using M062X–GD3 and double hybrid density functionals (B2PLYP–GD2, B2PLYP–GD3 and mPW2PLYP–GD2) are also taking into account. The basis set superposition error-corrected interaction energy for hydrogen bonded configurations ranges from − 5.27 to − 13.53 and − 5.25 to − 12.93 kcal/mol for TU and RU complexes respectively as calculated at M062X/6–311++G(df,pd) level. The charge transfer process within all of the TU and RU configurations were analyzed using Natural Bond Orbital (NBO) calculations. The nature of the interactions is analyzed with NBO and Atoms in Molecules (AIM) analysis at M062X/6–311++G(df,pd) and energy decomposition analysis at BP86–D3/TZ2P(ZORA)//M062X/6–311++G(df,pd) level of theory. The results confirm that the nature of the interactions is nearly electrostatic, with a contribution of about 51–56% of the total interaction energy. The orbital interactions (ΔEorb) for the considered TU and RU complexes have a contribution of about 24–38% of the total interaction energy. Based on the AIM and NBO results, the interactions were defined as electrostatic H-bonds with partially covalent character. In addition, correlation between interaction energies and vibrational frequency changes was investigated.

Piezoelectric beam generator based on MFC as a self-powered vibration sensor

A piezoelectric generator is a device used to convert mechanical energy into electrical energy. The basic element of the generator is made from piezoelectric material in which electrical energy is created as a result of deformations caused by reactions of mechanical structure of the generator. The generators, in which the main element is a cantilever beam constructed from basic material and from piezoelectric material, are one of structures, which are used to the energy harvesting from the mechanical vibrations. The piezoelectric generator are used as a part of self-powered wireless sensor in many scientific research. Such self-powered sensor consists of a sensor measuring selected parameter, a radio transmitter, and aforementioned piezoelectric beam generator. However, the piezoelectric beam generator has a limited application in supply a sensor, because the amount of electric energy generated by such generator does not exceed a few mili Watts and is achieved only if the vibration frequency of mechanical energy source equals the resonant frequency of a cantilever beam of piezoelectric generator. This problem is mainly tried to solve by modifications of the generator beam structure or by introducing additional elements with geometry adapted to the source of mechanical vibration. In contrast to these approaches, the article presents the experimental investigation on the action of self-powered wireless sensor in which a decrease of consumed energy amount was achieved through an using of piezoelectric beam generator, which power the radio transmitter, as a vibration sensor. The piezoelectric beam generator should product an amount of electric energy which is enough to supply only the radio transmitter. Such self-powered wireless sensor is dedicated to a vibration monitoring, in which the basic purpose is a detection of an appearance of the dangerous for building structure vibration. The presented self-powered vibration sensor based on a piezoelectric beam generator equipped with a standard energy harvesting circuit, a radio transmitter and a system of energy transfer control enabling power of a radio transmitter for established level of stored energy in capacitor allows a detection of dangerous vibrations for building structure, monitored by this sensor. In laboratory stand vibration amplitudes of the free end of piezoelectric generator were obtained by changes of vibration frequency and vibration amplitudes of its fixed end. In laboratory experiments the time among radio signal was measured for selected values of capacitor capacity and for changed vibration amplitude of free end of piezoelectric generator beam. On the basis of this experiments it was found that full robustness of tested self-powered sensor was achieved for the capacitor capacity equal to 440μF. The sending of a full package of data by such sensor can be realized only above a minimum value of the capacity of applied capacitor equals 220μF. The capacity of capacitor in piezoelectric self-powered vibration sensor should be selected between minimum value for which full packages of data are sending, in tested sensor it equals 220μF, and maximum values for which full robustness to disturbances is achieved. It was found that an increase of the capacitor capacity caused an improvement of data sending robustness to disturbances in radio transmission. The full robustness manifested the sending of every package of data. On the other hand, an increase of capacitor capacity led to the decrease of detection sensitivity of appearance of short-lived vibrations with the big amplitudes due to longer time of capacitor charging. It was noted that the increase of capacitor capacity did not improve the acting of such sensor in case of appearance of long-lived vibrations.

Vibration and Magnetic Field Sensing Using a Long-Period Grating

A long-period grating (LPG) written on a standard single mode fiber is investigated as a fiber optic sensor for vibration and magnetic field sensing. It is demonstrated the high sensitivity of the device to applied curvature and the possibility to monitor vibration in a wide range of frequencies from 30 Hz to 2000 Hz. The system was tested using intensity-based interrogation scheme, providing a frequency discrimination of 913 mHz. The goal of these tests was to evaluate the sensor as a passive vibration monitor in the detection of changes in resonant vibration frequencies of support infrastructures can provide information on its degradation. Furthermore, taking advantage of the intrinsic sensitivity to micro strain, alternating magnetic fields were also measured using an intensity-based interrogation scheme by coupling a Terfenol-D magnetostrictive rod to a pre-strained LPG sensor, providing a resolution below 5.61 $\mu \text{T}_{\mathrm {\mathbf {rms}}}/\surd $ Hz from 1.22 mTrms up to 2.53 mTrms.

Validation of a Vibrotactile Stimulation System Using the Wii Remote for Studies of Tactile Sensitivity

Background: Vibrotactile stimuli are widely used to study the functional characteristics of the haptic sense. Although many vibrotactile stimulators are commercially available, most are expensive. Objective: We developed a low-cost vibrotactile stimulation system using a Nintendo Wii Remote and a personal computer. In the present study, we examined the validity and accuracy of this vibrotactile stimulation system. Method: In the first experiment, we measured the linearity of vibration amplitude and changes in peak vibration frequency generated by the Wii Remote as a function of activation intensity. In the second experiment, the effect of vibrotactile stimuli applied to the dorsal surface of hand on two-point discrimination threshold at the index finger was examined in twelve participants. Results: The peak vibration frequency was about 150 Hz irrespective of vibration intensity, which would effectively activate fast adapting type II (FAII) cutaneous mechanical receptors. The two-point discrimination threshold measured at the third pad of the index finger decreased significantly when a near-threshold vibrotactile stimulus was applied to the dorsal hand, a response termed stochastic resonance (SR). These SR results are consistent with findings in the other sensory systems, such as auditory, visual, and somatosensory systems. Conclusion: This newly developed stimulation system produces controllable vibrotactile stimuli useful for study of the haptic sense.

A density functional theory study on the hydrogen bonding interactions between luteolin and ethanol.

Ethanol is one of the most commonly used solvents to extract flavonoids from propolis. Hydrogen bonding interactions play an important role in the properties of liquid system. The main objective of the work is to study the hydrogen bonding interactions between flavonoid and ethanol. Luteolin is a very common flavonoid that has been found in different geographical and botanical propolis. In this work, it was selected as the representative flavonoid to do detailed research. The study was performed from a theoretical perspective using density functional theory (DFT) method. After careful optimization, there exist nine optimized geometries for the luteolin-CH3CH2OH complex. The binding distance of X-H···O, and the bond length, vibrational frequency, and electron density changes of X-H all indicate the formation of the hydrogen bond in the optimized geometries. In the optimized geometries, it is found that: (1) except for the H2', H5', and H6', CH3CH2OH has formed hydrogen bonds with all the hydrogen and oxygen atoms in luteolin. The hydrogen atoms in the hydroxyl groups of luteolin form the strongest hydrogen bonds with CH3CH2OH; (2) all of the hydrogen bonds are closed-shell interactions; (3) the strongest hydrogen bond is the O3'-H3'···O in structure A, while the weakest one is the C3-H3···O in structure E; (4) the hydrogen bonds of O3'-H3'···O, O-H···O4, O-H···O3' and O-H···O7 are medium strength and covalent dominant in nature. While the other hydrogen bonds are weak strength and possess a dominant character of the electrostatic interactions in nature.

Factors of 18O/16O fractionation in corundum estimated from the calculation of isotopic shifts on vibration frequencies

The β-factors of corundum were estimated on the basis of DFT calculations of vibrational frequency changes due to 16O–18O isotope substitution in a harmonic approximation using an all-electron Gaussian-type basis set and the B3LYP hybrid functional (the CRYSTAL program). Calculations were performed accounting for eight phonon wave vectors within the first Brillouin zone. The results are approximated by the relation 1000ln β crn = 9.19874x–0.12326x 2 + 0.00213x 3 (x = 106/T(K)2, 400 < T(K) < 1300), which can be used in isotope geochemical studies in combination with the known temperature effects on the β-factors of other phases.

Viscoelastic Drag Forces and Crossover from No-Slip to Slip Boundary Conditions for Flow near Air-Water Interfaces.

The "free" water surface is generally prone to contamination with surface impurities, be they surfactants, particles, or other surface active agents. The presence of such impurities can modify flow near such interfaces in a drastic manner. Here we show that vibrating a small sphere mounted on an atomic force microscope cantilever near a gas bubble immersed in water is an excellent probe of surface contamination. Both viscous and elastic forces are exerted by an air-water interface on the vibrating sphere even when very low doses of contaminants are present. The viscous drag forces show a crossover from no-slip to slip boundary conditions while the elastic forces show a nontrivial variation as the vibration frequency changes. We provide a simple model to rationalize these results and propose a simple way of evaluating the concentration of such surface impurities.

Temperature Sensitivity and Shape Optimization of Solid-State Wave Gyroscopes

We analyze the change of angular gain and vibration frequency of the solid-state wave gyroscopes as a result of geometry perturbations due to thermal expansion. We analyze sensitivity of the device to the thermal expansion effects by an isoparametric finite-element analysis method, and we analyze the sensitivity to thermal changes in the material properties assuming a linear dependence on temperature. We quantify these sensitivities for common device geometries, and use our analysis as the basis for a local optimization problem that minimizes the temperature sensitivity as a function of device shape.

Role of reduced precursor and solvolytic reagent molar ratio on preparation and properties of ionogel

In the present study, ionogels have been synthesized by immobilizing IL (1-ethyl-3-methylimidazolium tetrafluoroborate) in silica gel matrices using non-aqueous route. In this process, tetraethyl orho-silane (TEOS) as a precursor to silicon dioxide and formic acid as a solvolytic gelating reagent in reduced molar ratio 1:4 were used. We find that reduced molar concentration of formic acid results the formation of ionogels having less number of closed pores (totally isolated from their neighbours), larger density and stable monolithic form. TEM and SEM measurements are used to visualize the morphology of sample and closed pores present in the sample. N2-sorption measurement is used to measure the pore parameters of the silica matrices which shows the mesoporous structure. DSC and TGA results show the change in phase transition temperature and thermal stability of IL upon confinement in silica matrices. Moreover, ionic conductivity of bulk and confined IL is measured using impedance spectroscopy and it has been found that it increases with increasing the temperature as well as concentration of IL in ionogels. Apart from these characterization techniques, ionogels have been characterized using FTIR and fluorescence spectroscopy which exhibit the change in vibrational frequencies and fluorescence behaviour of confined IL.

Theoretical Investigation on the Substituent Effect of Halogen Atoms at the C8 Position of Adenine: Relative Stability, Vibrational Frequencies, and Raman Spectra of Tautomers.

We have theoretically investigated the substituent effect of adenine at the C8 position with a substituent X = H, F, Cl, and Br by using the density functional theory (DFT) at the B3LYP/6-311+G(d, p) level. The aim is to study the substituent effect of halogen atoms on the relative stability, vibrational frequencies, and solvation effect of tautomers. Our calculated results show that for substituted adenine molecules the N9H8X tautomer to be the most stable structure in gas phase at the present theoretical level. Here N9H8X denotes the hydrogen atom binds to the N9 position of imidazole ring and X denotes H, F, Cl, and Br atoms. The influence of the induced attraction of the fluorine substituent is significantly larger than chlorine and bromine ones. The halogen substituent effect has a significant influence on changes of vibrational frequencies and Raman intensities.

Editorial: Optogenetic Tools in the Molecular Spotlight.

Editorial: Optogenetic Tools in the Molecular Spotlight.

Red-Shifting versus Blue-Shifting Hydrogen Bonds: Perspective from Ab Initio Valence Bond Theory.

Both proper, red-shifting and improper, blue-shifting hydrogen bonds have been well-recognized with enormous experimental and computational studies. The current consensus is that there is no difference in nature between these two kinds of hydrogen bonds, where the electrostatic interaction dominates. Since most if not all the computational studies are based on molecular orbital theory, it would be interesting to gain insight into the hydrogen bonds with modern valence bond (VB) theory. In this work, we performed ab initio VBSCF computations on a series of hydrogen-bonding systems, where the sole hydrogen bond donor CF3H interacts with ten hydrogen bond acceptors Y (═NH2CH3, NH3, NH2Cl, OH(-), H2O, CH3OH, (CH3)2O, F(-), HF, or CH3F). This series includes four red-shifting and six blue-shifting hydrogen bonds. Consistent with existing findings in literature, VB-based energy decomposition analyses show that electrostatic interaction plays the dominating role and polarization plays the secondary role in all these hydrogen-bonding systems, and the charge transfer interaction, which denotes the hyperconjugation effect, contributes only slightly to the total interaction energy. As VB theory describes any real chemical bond in terms of pure covalent and ionic structures, our fragment interaction analysis reveals that with the approaching of a hydrogen bond acceptor Y, the covalent state of the F3C-H bond tends to blue-shift, due to the strong repulsion between the hydrogen atom and Y. In contrast, the ionic state F3C(-) H(+) leads to the red-shifting of the C-H vibrational frequency, owing to the attraction between the proton and Y. Thus, the relative weights of the covalent and ionic structures essentially determine the direction of frequency change. Indeed, we find the correlation between the structural weights and vibrational frequency changes.

Oil shale separation using a novel combined dry beneficiation process

Significant mineral impurities are produced during oil shale mining. However, inorganic minerals can be partially discarded, with an improvement in oil shale quality, through physical separation methods. Based on analysis of physical properties of oil shale, this paper firstly proposes a separation process combining compound dry cleaning and vibrated air dense medium fluidized bed (VADMFB) separation, for separation of oil shale across the full size range of 100–0mm. We systematically analyzed the effects of changes in vibration amplitude and frequency on separation results and oil ratios for both systems. When oil shale with a size range of 100–6mm was separated using compound dry cleaning, using optimal vibrational parameters of f=53Hz and A=3.6mm, yields of concentrate was 20.49%, respectively, with corresponding oil content of 11.20%, The probable error (E) was 0.155–0.21 with the largest oil content segregation degree. Oil shale with a size fraction of 6–0mm was separated in a VADMFB separator at optimal vibrational conditions (f=36Hz and A=2.5mm). Resultant yields of concentrate was 21.70%, respectively, with corresponding oil content of 10.1%. E was 0.16–0.185 with the largest oil ratio segregation intensity. This study thus confirms that the proposed combined dry beneficiation process can effectively separate oil shale along the full size range of 100–0mm.

A DFT study on the absorption mechanism of vinyl chloride by ionic liquids

To find efficient method to control the release of vinyl chloride (VC) to the atmosphere, the absorption mechanisms of VC in four ionic liquids (ILs) were investigated, including 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF4]), 1-butyl-3-methyl imidazolium hexafluorophosphate ([BMIM][PF6]), tetramethyl guanidinelactate (TMGL) and 4-bis(2-hydroxypropyl)-1,1,3,3-tetramethyl guanidinium tetrafluoroborate ([TMGHPO2][BF4]). The structures of ILs and corresponding complexes were optimized at B3LYP/6-311++G(d,p) level. According to the interaction energy, [TMGHPO2][BF4] showed the best absorption capacity of VC, which was consistent with the experimental results. Computational results also indicated that the absorption of VC in guanidinium IL was a physical adsorption. The analysis of vibration frequency changes in the absorption process indicated that the formation of hydrogen bonds between VC and [BF4]− weakened the hydrogen-bonding interaction between [BF4]− and [TMGHPO2]+.